is it safe to assume that flexing any muscle, undetectable to the eye and the sensors on your body, will alter your GSR and blood pressure? like say flexing the muscle people use to move their ears, except your ears dont move and there is perceptible flex in your neck region? would this be comparable to tightening the sphincter?
While I do not know how effective attempting to "wiggle one's ears" would be at producing scorable reactions, such reactions can definitely be produced by flexing muscles other than the anal sphincter. For example, a countermeasure study by Charles Honts and others found pressing the toes to the floor to be effective. (See the bibliography of The Lie Behind the Lie Detector (http://antipolygraph.org/lie-behind-the-lie-detector.pdf) for citation and abstract.)
To counter this, some polygraph instruments come equipped with a strain guage attached to the chair or a sensor pad on the seat (and in some cases, the arm rests, too) that might alert the polygrapher to the use of such physical countermeasures. Illustrations of such devices are found in the message thread, Counter-Countemeasure Techniques (https://antipolygraph.org/forum/index.php?topic=1352.msg10796#msg10796).